In recent and future radio systems, there is generally an increasing need to exploit the radio spectrum as effectively as possible. In recent and future radio communication systems, there is also an increasing need to enable higher data rates. In view thereof, multi-carrier radio systems, especially multi-band multi-carrier radio systems, are being developed in order to cope with such needs.
FIG. 1 shows a graph illustrating a multi-band multi-carrier scenario, for which embodiments of the present invention are applicable. As shown in FIG. 1, multiple carriers from different frequency bands may be used for radio transmission purposes in a combined or aggregated manner.
For example, such a multi-band multi-carrier scenario approach is currently used in dual-band dual-carrier (DB-DC) or dual-band four-carrier (DB-4C) HSDPA and LTE inter-band carrier aggregation (CA). In 3GPP specifications, certain band configurations are specified in this regard. For example, band combinations I+VIII, II+IV, I+V, I+XI, and II+V are currently specified for DB-DC HSDPA and DB-4C HSDPA, while roughly 20 inter-band combinations (e.g. bands 4+13, 20+7, 2+17, 3+20, 2+MediaFlo, 4+MediaFlo, 1+18, 1+19, 4+17, 4+12, 3+7, 5+12, 5+17, 1+7, 4+7, 5+MediaFlo, 4+5, 3+5, 8+20, 11+18, 1+21) are currently specified (and dedicated for specific operators) for inter-band CA.
Currently, a single direct-conversion receiver is typically utilized in terminals of recent radio (communication) systems. Examples for the utilization of DCR-type receivers in cellular systems involve UEs in GSM, WCDMA, HSPA, and single-carrier LTE modes (Rel-7/8/9).
FIG. 2 shows a schematic block diagram of a topology of a conventional direct-conversion receiver (DCR).
As evident From FIG. 2, a received radio signal is preselected by a pre-select (band-pass) filter, and the thus preselected radio signal is amplified in a low-noise amplifier (LNA) before being down-converted, e.g. to zero intermediate frequency (IF) for single-carrier reception and to low intermediate frequency (IF) for dual-carrier reception. For phase- and frequency-modulated signals, the down-conversion is to be performed with down-conversion mixers (MIX) controlled by a quadrature local oscillator (LO) signal to prevent signal sidebands from aliasing on one another. In each quadrature receive path, prior to analog-to-digital conversion by an analog-to-digital converter (ADC), the signal is low-pass filtered by a low-pass filter (LPF) and amplified by an amplifier (AMP) such that the signal level for the ADC is at a sufficient level.
The basic problem with a single-RX-chain topology of a DCR-type receiver, as shown in FIG. 2, is that it is not able to (concurrently) receive radio signals of a multi-band multi-carrier scenario such as an RF allocation shown in FIG. 1. The reception of two (or, possibly even more) non-contiguous component carriers causes several design challenges for a receiver containing one RX chain only.
However, from an integrated circuit development point of view, DCR-type receivers have several advantages compared to other receiver types, such as low complexity and power consumption, small silicon area, and a low number of off-chip components. Further, utilization of DCR-type receivers for terminals of recent and future radio systems is also beneficial in terms of backward compatibility and multi-mode operability. For example, this is evident when considering that e.g. a Rel-10 NC-HSDPA (or non-contiguous LTE) capable UE may also be configured for lower data rates and single-carrier operation, and user expectations would be for similar or better battery life than legacy UEs when operating at lower data rates (i.e. in non-carrier aggregation mode).
Accordingly, it is desirable and also to be expected that DCR-type receivers are also utilized for multi-band multi-carrier scenarios, such as e.g. with DB-DC/DB-4C HSDPA and/or multi-carrier LTE modes (Rel-10 and beyond). Yet, such receivers would need to be able to (concurrently) receive inter-band non-contiguous carriers.
The aforementioned problem could be addressed by handling multiple carriers of multiple frequency bands in separate RX chains of DCR type, both having a LO signal of its own. This is depicted in FIG. 3, where a multi-band multi-carrier scenario with two separate local oscillator frequencies is illustrated, for which embodiments of the present invention are applicable.
Possible solutions for a receiver, which is able to handle a dual-band dual-carrier reception concurrently, could be based on two separate single-carrier RX chains of DCR-type.
FIG. 4 shows a schematic block diagram of a first topology of a receiver with separate receive paths of conventional direct-conversion receivers, wherein two separate RFICs are utilized. FIG. 5 shows a schematic diagram of a second topology of a receiver with separate receive paths of conventional direct-conversion receivers, wherein a single RFIC is utilized.
In the topology according to FIG. 4, there is a disadvantage that the cost of the platform clearly increases, since two separate RFICs with additional power management circuits, crystal oscillators, input matching components, decoupling components etc. are needed. In addition to an additional RX chain, there would also be lots of redundant hardware added with the drawback of increased PWB area. Thus, this would be an undue and expensive solution to realize a concurrent dual-band receiver.
In the topology according to FIG. 5, the number of RX chains is doubled in a single RFIC. Typically, the number of LNA inputs in a single RFIC is high—normally 6-10 per RX chain (i.e. 12-20 in total when main and diversity receptions are calculated together in a diversity receiver). The placing of LNA inputs on the RFIC die is already challenging and routing to package pins requires a number of trade-offs to be solved, thus degrading the LNA performance. In addition, depending on the number of RFIC inputs, the count of the external matching components can become high, thus being an expensive solution. Thus, this would be an undue and expensive solution to realize a concurrent dual-band receiver.
FIG. 6 shows a schematic block diagram of a topology of a multi-input configurable receiver based on a conventional direct-conversion receiver.
The topology shown in FIG. 6 represents a simplified topology of a hardware/performance-optimized DCR-type receiver which is able to support multiple carriers on multiple bands. To this end, there are n LNA input stages dedicated to support low-bands (LB), illustrated by a dash-dotted block and denoted as LNALB, and m LNA input stages dedicated to support high-bands (HB), illustrated by a dash-dotted block and denoted as LNAHB. The carrier signal from an active input is guided to a corresponding load (ZL,LB for low-bands or ZL,HB for high-bands). ZM represents an interface between LNA and mixer portions. The interface ZM can consist of a passive network and separate transconductance (gm) stages, implementing several gain steps, and/or have separate signal paths for I and Q branches, etc. Low-band and high-band LNA loads (ZL,LB, ZL,HB) are typically followed by separate mixer cores. This leads to sufficient overall performance and minor layout area increase, since mixer cores occupy only a fairly small die area and the LNA-mixer interface is critical for receiver performance. Therefore, LB/HB signal paths are typically combined after down-conversion to intermediate frequency in the mixer stage.
However, the receiver according to FIG. 6 exhibits multiple RX chains on the input side only, whilst these converge (by virtue of the switches after the mixer stage) to a single RX chain on the output side. Thus, this receiver topology is also not capable of concurrently receiving and outputting to the digital data path carrier signals of multiple carriers.
Accordingly, there is currently no viable solution to the aforementioned problems.
Thus, there is a desire to provide a receiver circuit for concurrent reception of multiple carriers and a receiver using the same, which are capable of (concurrently) receiving multiple carriers in a multi-band multi-carrier scenario on the basis of a DCR-type topology.